Detection of specific autoantigens in prediabetic individuals has been used as a predictive marker to identify, before clinical onset and significant xcex2-cell loss has occurred, those at greater risk of developing IDDM (Gorsuch et al., Lancet 2: 1363-65, 1981; Baekkeskov et al., J. Clin. Invest. 79: 926-34, 1987; Johnstone et al., Diabetologia 32: 382-86, 1989; Ziegler et al., Diabetes 38: 1320-25, 1989; Baekkeskov et al., Nature (Lond) 347: 151-56, 1990; Bonifacio et al., Lancet 335: 147-49, 1990; and Bingley et al. Diabetes 43: 1304-10, 1994).
Antibodies to the 40 kD, and more particularly the 37 kD, ICA fragments are detected when clinical onset of IDDM is imminent and are found to be closely associated with IDDM development (Christie et al., Diabetes 41: 782-87, 1992). Diabetic sera containing antibodies specific to the 40 kD fragment were recently found to bind to the intracellular domain of the protein tyrosine phosphatase, IA-2/ICA512 (Lu et al., Biochem. Biophys. Res. Comm. 204: 930-36, 1994; Lan et al., DNA Cell Biol. 13: 505-14, 1994; Rabin et al., J. Immunol. 152: 3183-88, 1994; Payton et al., J. Clinc. Invest. 96: 1506-11, 1995; and Passini et al., Proc. Natl. Acad. Sci. USA 92: 9412-16, 1995). Antibodies specific to the 37 kD fragment are thought to bind either to a posttranslational in vivo modification of IA-2/ICA512 or a different, but probably related, protein precursor (Passini et al., ibid.).
ICA 512 was initially isolated as an autoantigen from an islet cell cDNA library, and was subsequently shown to be related to the receptor-linked protein tyrosine phosphatase family (Rabin et al., ibid.). ICA 512 was later found to be identical to a mouse and human protein tyrosine phosphatase, IA-2, isolated from brain and insulinoma cDNA libraries (Lu et al., ibid.; and Lan et al., ibid.).
Detection of diabetes-associated autoantigens, especially combinations of autoantigens, genotypes, such as HLA DR and HLA DQ, and loci, such as the polymorphic region in the 5xe2x80x2 flanking region of the insulin gene; in prediabetic individuals have been shown to be useful predictive markers of IDDM, see for example, Bell et al., (Diabetes 33:176-83, 1984); Sheehy et al., (J. Clin. Invest. 83:830-35, 1989); and Bingley et al., (Diabetes 43: 1304-10, 1994). There is therefore a need in the art for autoantigens that would serve to improve detection and diagnosis of IDDM. The present invention fulfills this need by providing novel autoantigens as well as related compositions and methods. The autoantigens of the present invention represent a new xcex2-cell antigen. The present invention also provides other, related advantages.
The present invention provides an isolated polynucleotide which forms an immune complex with an autoantibody from a patient at risk of or predisposed to develop IDDM, comprising a DNA segment encoding a mammalian islet cell antigen polypeptide of SEQ ID NO:16 from Leu, amino acid residue 636 to Gln, amino acid residue 1012. The invention also provides a mammalian islet cell antigen polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818. The invention also provides allelic variants of these polypeptides. Within one aspect of the invention, the isolated polynucleotide encodes a mammalian islet cell antigen polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418, to Gln, amino acid residue 818. Within another aspect of the invention, the isolated polynucleotide encodes a mammalian islet cell antigen polypeptide of SEQ ID NO:16 from Phe, amino acid residue 612, to Gln, amino acid residue 1012. The invention further provides allelic variants of these polypeptides. Within another aspect, the isolated polynucleotide encoding a polypeptide of SEQ ID NO:16 from Ala, amino acid residue 1, to Gln, amino acid residue 1012. Within another aspect, the isolated polynucleotide encoding a polypeptide of SEQ ID NO:22 from His, amino acid residue 1, to Gln, amino acid residue 818. The invention further provides allelic variants of these polypeptides. Within another aspect, the isolated polynucleotide is a DNA molecule comprising a coding sequence corresponding to SEQ ID NO:21 from nucleotide 1325 to nucleotide 2455. In still another aspect, the DNA molecule comprises a coding sequence corresponding to SEQ ID NO:15 from nucleotide 1909 to nucleotide 3039. The invention also provides allelic variants of these molecules. The invention further provides complements of polynucleotide molecules which specifically hybridize to these molecules. In yet another aspect, the isolated polynucleotide is a DNA molecule comprising a coding sequence corresponding to SEQ ID NO:21 from nucleotide 1254 to nucleotide 2455. Within another aspect, the isolated polynucleotide is a DNA molecule comprising a coding sequence corresponding to SEQ ID NO:15 from nucleotide 1837 to nucleotide 3039. The invention also provides allelic variants of these molecules. The invention further provides complements of polynucleotide molecules which specifically hybridize to these molecules. In still another aspect, the DNA molecule comprises a coding sequence corresponding to SEQ ID NO:15 from nucleotide 4 to nucleotide 3039. In still another aspect, the DNA molecule comprises a coding sequence corresponding to SEQ ID NO:21 from nucleotide 2 to nucleotide 2455. The invention also provides allelic variants of these molecules. The invention further provides complements of polynucleotide molecules which specifically hybridize to these molecules. The invention also provides an isolated polynucleotide molecule which encodes a complete coding sequence of a mammalian islet cell antigen polypeptide comprising the sequence of SEQ ID NO:22 from Leu, amino acid residue 442 to Arg, amino acid residue 738. The invention also provides mammalian islet cell antigens that are primate islet cell antigens.
The invention also provides DNA constructs comprising a first DNA segment encoding a human islet cell antigen polypeptide operably linked to additional DNA segments required for the expression of the first DNA segment. The invention further provides a first DNA segment that is an isolated polynucleotide molecule encoding a human islet cell antigen polypeptide comprising the amino acid sequence of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818. The invention also provides a first DNA segment that is an isolated polynucleotide molecule encoding a human islet cell antigen polypeptide comprising the amino acid sequence of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818. Within another aspect, the invention provides a first DNA segment that is an isolated polynucleotide molecule encoding a human islet cell antigen polypeptide comprising the amino acid sequence of SEQ ID NO:22 from His, amino acid residue 1, to Gln, amino acid residue 818. The invention further provides host cells containing such DNA constructs, as well as methods for producing human islet cell antigen polypeptides comprising the steps of culturing such host cell and isolating the human islet cell antigen polypeptide.
The invention further provides isolated mammalian islet cell antigen polypeptides, wherein said isolated mammalian islet cell antigen polypeptide forms an immune complex with an autoantibody from a patient at risk of or predisposed to develop IDDM comprising the amino acid sequence of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818. The invention further provides isolated mammalian islet cell antigen polypeptides comprising the amino acid sequence of SEQ ID NO:16 from Leu, amino acid residue 636 to Gln, amino acid residue 1012.
The invention also provides isolated polypeptides of SEQ ID NO:16 from Phe, amino acid residue 612 to Gln, amino acid residue 1012. The invention also provides isolated polypeptides of SEQ ID NO:22 from Phe, amino acid residue 418, to Gln, amino acid residue 818. The invention further provides isolated polypeptides of SEQ ID NO:16 from Ala, amino acid residue 1 to Gln, amino acid residue 1012. The invention also provides isolated polypeptides of SEQ ID NO:22 from His, amino acid residue 1, to Gln, amino acid residue 818. The invention further provides allelic variants of these polypeptides. The invention still further provides an isolated polypeptide which is a full length mammalian islet cell antigen protein comprising the sequence of SEQ ID NO:22 from Leu, amino acid residue 442 to Arg, amino acid residue 738. The invention also provides mammalian islet cell antigens that are primate islet cell antigens.
Within yet another aspect of the invention is provided a method for determining the presence of an autoantibody to a human islet cell antigen polypeptide in a biological sample, comprising the steps of contacting the biological sample with the human islet cell antigen polypeptide, which comprises an amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gln, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof, under conditions conducive to immune complex formation, and detecting the presence of immune complex formation between the human islet cell antigen polypeptide and the autoantibody to a human islet cell antigen, thereby determining the presence of autoantibodies to the human islet cell antigen in the biological sample. The invention further provides human islet cell antigen polypeptides that are detectably labeled.
Within a further embodiment the invention provides a method for predicting the clinical course of diabetes in a patient, comprising testing a biological sample from a patient for the presence of human islet cell antigen polypeptides comprising the amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gln, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof, wherein the polypeptide forms an immune complex with an autoantibody from a patient at risk of or predisposed to develop IDDM, and classifying the patient for clinical course of diabetes based on the presence or absence of human islet cell antigens in the sample. The invention further provides a method of predicting the clinical course of IDDM by testing one or more additional predictive markers associated with risk of or protection from IDDM. The invention provides methods of predicting the clinical course where the predictive marker is an autoantibody to an antigen selected from the group consisting of GAD65, IA-2/ICA512 or insulin. The invention also provides methods wherein the predictive marker is a genotype selected from the group consisting of HLA DR and HLA DQ. The invention also provides methods wherein the predictive marker is a polymorphic region in the 5xe2x80x2 flanking region of a human insulin gene.
The invention also provides a method for treating a patient to prevent an autoimmune response to a human islet cell antigen polypeptide comprising inducing immunological tolerance in the patient by administering a mammalian islet cell antigen polypeptide comprising the amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gin, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof, that specifically binds a human islet cell antigen receptor on immature or mature T or B lymphocytes.
The invention also provides oligonucleotide probes of at least about 16 nucleotides, wherein which the oligonucleotide is at least 85% homologous to a sequence of the mammalian islet cell antigen DNA sequence of SEQ ID Nos:15 or 21.
The invention further provides isolated antibodies which specifically bind to human islet cell antigen polypeptides which comprise the amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gln, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof. Within another aspect, the invention provides monoclonal antibodies. Within yet another aspect, the invention provides a hybridoma which produces the monoclonal antibody.
The invention also provides a diagnostic kit for use in detecting autoantibodies to pancreatic xcex2-islet cells, comprising a container containing an islet cell antigen polypeptide comprising an amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gln, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof, wherein the polypeptide forms an immune complex with autoantibodies from a patient at risk of or predisposed to develop IDDM, and one or more containers containing additional reagents.
Within another embodiment of the invention is provided a pharmaceutical composition comprising an islet cell antigen comprising an amino acid sequence selected from the group consisting of a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 81, a polypeptide of SEQ ID NO:22 from Phe, amino acid residue 418 to Gln, amino acid residue 818, a polypeptide of SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818, and allelic variants thereof, in combination with a pharamceutically acceptable carrier or vehicle.
Within a further embodiment of the invention is provided a method for monitoring the disease state in a patient comprising testing a biological sample from a patient for the presence of human islet cell antigen post-translationally modified polypeptides, determining the concentration of the peptides and correlating the peptide levels in the sample with the disease state in the patient. The invention provides that the human islet cell antigen post-translationally modified polypeptide comprises the sequence of SEQ ID NO:22 from His, amino acid residue 1 to Glu, amino acid residue 227. The invention further provides that the biological sample is plasma or serum.
Within yet a further embodiment, the invention provides a method for monitoring the disease state in a patient comprising exposing T cells to islet cell antigen 1851 peptides, detecting T and correlating T cell reactivity with disease state. The invention provides that the T cells are from peripheral blood mononuclear cells from a prediabetic patient. The invention further provides that the disease state is conversion from prediabetes to diabetes.
Prior to setting forth the invention, it may be helpful to an understanding thereof to set forth definitions of certain terms to be used hereinafter:
Allelic variantxe2x80x94Any of two or more alternative forms of a gene occupying the same chromosomal locus. Allelic variation arises naturally through mutation, and may result in phenotypic polymorphism within populations. Gene mutations can be silent (no change in the encoded polypeptide) or may encode polypeptides having altered amino acid sequence. The term allelic variant is also used herein to denote a protein encoded by an allelic variant of a gene.
Biological samplexe2x80x94A sample that is derived from or contains cells, cell components or cell products, including, but not limited to, cell culture supernatants, cell lysates, cleared cell lysates, cell extracts, tissue extracts, blood plasma, serum, and fractions thereof, from a patient.
Complements of polynucleotide moleculesxe2x80x94
Polynucleotide molecules having a complementary base sequence and reverse orientation as compared to a reference sequence. For example, the sequence 5xe2x80x2 ATGCACGGG 3xe2x80x2 is complementary to 5xe2x80x2 CCCGTGCAT 3xe2x80x2.
Immune Complex Formationxe2x80x94A noncovalently bound molecule formed between an antigen and an antibody specific for that antigen, resulting in an extensively cross-linked mass. Conditions conducive to complex formation are known in the art and easily adaptable by those skilled in art, for example, the degree of complex formation is in proportion to the relative amounts of available antigen and antibody. Such complexes can be used, for example, to identify and/or quantify the presence of either antigen or antibody in a biological sample, identify and characterize particular antibodies in tissues and cells, or to stimulate an immune response.
Isolatedxe2x80x94When applied to a protein the term xe2x80x9cisolatedxe2x80x9d indicates that the protein is found in a condition other than its native environment, such as apart from blood and animal tissue. In a preferred form, the isolated protein is substantially free of other proteins, particularly other proteins of animal origin. It is preferred to provide the proteins in a highly purified form, i.e. greater than 95% pure, more preferably greater than 99% pure. When applied to a polynucleotide molecule the term xe2x80x9cisolatedxe2x80x9d indicates that the molecule is removed from its natural genetic milieu and is thus free of other extraneous or unwanted coding sequences, and is in a form suitable for use within genetically engineered protein production systems. Such isolated molecules are those that are separated from their natural environment and include cDNA and genomic clones. Isolated DNA molecules of the present invention are free of other genes with which they are ordinarily associated and may include naturally occurring 5xe2x80x2 and 3xe2x80x2 untranslated regions such as promoters and terminators, the identification of such will be evident to one of ordinary skill in the art (see for example, Dynan and Tijan, Nature 316: 774-78, 1985).
Operably linkedxe2x80x94Indicates that the segments are arranged so that they function in concert for their intended purposes, e.g., transcription initiates in the promoter and proceeds through the coding segment to the terminator.
The DNA sequences encoding the polypeptides of the present invention were unexpectedly identified during screening of a primate islet cell cDNA library, and human insulinoma cDNA, for autoantigens toward human diabetic sera. Analysis of the macaque cDNA clones revealed a unique, previously unknown islet cell antigen which contained regions of homology to the protein tyrosine phosphatase family, especially the protein tyrosine phosphatase IA2/ICA512. This novel islet cell antigen has been designated 1851 or ICA512xcex2.
The present invention provides islet cell antigen polypeptides which are xcex2-cell autoantigens. These autoantigens were reactive with human prediabetic and diabetic sera. The invention also provides methods for using the islet cell antigen polypeptides for the detection, diagnosis, and treatment of IDDM.
Representative islet cell antigen polypeptides of the present invention comprise the amino acid sequences in SEQ ID NOs:4, 16 or 22 and/or are encoded by polynucleotide sequences comprising the sequences of SEQ ID NOs:3, 15 and 21 and form an immune complex with autoantibodies from a patient at risk of or predisposed to develop IDDM. The islet cell antigen polypeptides of the present invention are preferably from mammals, especially primates including humans. Preferred polypeptides of the present invention include isolated polypeptides selected from the group consisting of a polypeptide of SEQ ID NO:2 from Leu, amino acid residue 265, to Gln amino acid residue 641. The invention also provides polypeptides of SEQ ID NO:2 from Glu, amino acid residue 1, to Gln, amino acid residue 641. The invention further provides macaque polypeptides of SEQ ID NO:16 from Ala, amino acid residue 1 to Gln, amino acid residue 1012 and human polypeptides of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818 and SEQ ID NO:22 from His, amino acid residue 1 to Gln, amino acid residue 818. The invention further provides allelic variants and isolated sequences that are substantially identical to the representative polypeptide sequences of SEQ ID NOs:2, 16 and 22 and their species homologs. The term xe2x80x9csubstantially identicalxe2x80x9d is used herein to denote proteins having 50%, preferably 60%, more preferably 70%, and most preferably at least 80%, sequence identity to the representative sequences shown in SEQ ID NO:2, 16 or 22 or its species homologs. Within preferred embodiments, such proteins will be at least 90% identical, and most preferably 95% or more identical, to SEQ ID NO:2, 16 or 22 or their species homologs.
Percent sequence identity is determined by conventional methods. See, for example, Altschul et al., Bull. Math. Bio. 48: 603-616, 1986; Pearson and Lipman, Proc. Natl. Acad. Sci. USA 85:2444-2448, 1988; and Henikoff and Henikoff, Proc. Natl. Acad. Sci. USA 89:10915-10919, 1992. Briefly, two amino acid sequences are aligned to optimize the alignment scores using a gap opening penalty of 10, a gap extension penalty of 1, and the xe2x80x9cblosum 62xe2x80x9d scoring matrix of Henikoff and Henikoff (ibid.) as shown in Table 1 (amino acids are indicated by the standard one-letter codes). The percent identity of the optimum alignment is then calculated as:
            Total      ⁢              xe2x80x83            ⁢      number      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      identical      ⁢              xe2x80x83            ⁢      matches                                            [                          length              ⁢                              xe2x80x83                            ⁢              of              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              longer              ⁢                              xe2x80x83                            ⁢              sequence              ⁢                              xe2x80x83                            ⁢              plus              ⁢                              xe2x80x83                            ⁢              the                                                                        number            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            gaps            ⁢                          xe2x80x83                        ⁢            introduced            ⁢                          xe2x80x83                        ⁢            into            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            longer                                                                          sequence              ⁢                              xe2x80x83                            ⁢              in              ⁢                              xe2x80x83                            ⁢              order              ⁢                              xe2x80x83                            ⁢              to              ⁢                              xe2x80x83                            ⁢              align              ⁢                              xe2x80x83                            ⁢              the              ⁢                              xe2x80x83                            ⁢              two              ⁢                              xe2x80x83                            ⁢              sequences                        ]                                xc3x97  100
Substantially identical proteins are characterized as having one or more amino acid substitutions, deletions or additions. These changes are preferably of a minor nature, that is conservative amino acid substitutions (see Table 2) and other substitutions that do not significantly affect the folding or activity of the protein; small deletions, typically of one to about 30 amino acids; amidation of the amino- or carboxyl-terminal; and small amino- or carboxyl-terminal extensions, such as an amino-terminal methionine residue, a small linker peptide of up to about 20-25 residues, or a small extension that facilitates purification, such as a poly-histidine tract, an antigenic epitope or a binding domain. See, in general, Ford et al., Protein Expression and Purification 2: 95-107, 1991, which is incorporated herein by reference.
Essential amino acids in the polypeptides of the present invention can be identified according to procedures known in the art, such as site-directed mutagenesis or alanine-scanning mutagenesis (Cunningham and Wells, Science 244, 1081-85, 1989). In the latter technique, single alanine mutations are introduced at every residue in the molecule, and the resultant mutant molecules are tested for biological activity (e.g. protein tyrosine phosphatase activity, Strueli et al., EMBO J. 9: 2399-407, 1990, or binding to autoantibodies in prediabetic or diabetic sera) to identify amino acid residues that are critical to the activity of the molecule. Sites of ligand-receptor interaction can also be determined by analysis of crystal structure as determined by such techniques as nuclear magnetic resonance, crystallography or photoaffinity labeling. See, for example, de Vos et al., Science 255:306-12, 1992; Smith et al., J. Mol. Biol. 224:899-904, 1992; Wlodaver et al., FEBS Lett. 309:59-64, 1992.
Multiple amino acid substitutions can be made and tested using known methods of mutagenesis and screening, such as those disclosed by Reidhaar-Olson and Sauer (Science 241:53-57, 1988) or Bowie and Sauer (Proc. Natl. Acad. Sci. USA 86:2152-156, 1989). Briefly, these authors disclose methods for simultaneously randomizing two or more positions in a protein, selecting for functional protein, and then sequencing the mutagenized proteins to determine the spectrum of allowable substitutions at each position. These methods allow the rapid determination of the importance of individual amino acid residues in a protein of interest, and can be applied to proteins of unknown structure.
The present invention further provides isolated polynucleotide molecules encoding islet cell antigen polypeptides which form immune complexes with autoantibodies from a patient at risk of or predisposed to develop IDDM. Useful polynucleotide molecules in this regard include mRNA, genomic DNA, cDNA and synthetic DNA. For production of recombinant islet cell antigen polypeptides, cDNA is preferred. The invention provides an isolated polynucleotide molecule wherein the molecule is a DNA molecule comprising a coding sequence corresponding to SEQ ID NO:1 from nucleotide 795 to nucleotide 1922. The invention also provides a DNA molecule comprising a coding sequence corresponding to SEQ ID NO:1 from nucleotide 1 to nucleotide 2168. The invention also provides a DNA molecule comprising a coding sequence corresponding to nucleotide 4 to nucleotide 3039 of SEQ ID NO: 15. The invention also provides DNA molecules from nucleotide 1325 to nucleotide 2455, from nucleotide 1254 to nucleotide 2455 and from nucleotide 2 to nucleotide 2544 of SEQ ID NO:21. The invention also provides allelic variants of the sequences shown in SEQ ID NOs:1, 15 or 21, and polynucleotide molecules that specifically hybridize to allelic variants. Such polynucleotide molecules will hybridize to the representative DNA sequences of SEQ ID NOs:1, 15, 21 or their allelic variants under stringent conditions (Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., 1989). As used herein, the term xe2x80x9cstringent conditionsxe2x80x9d refers to hybridizing conditions that employ low ionic strength and high temperature for washing, for example, 0.015 M NaCl/0.0015 M sodium citrate/0.1% SDS at 50xc2x0 C.; employ during hybridization a denaturing agent such as formamide, for example, 50% (vol/vol) formamide with 0.1% polyvinylpyrrolidone/50 mM sodium citrate at 42xc2x0 C.; or employ 50% formamide, 5xc3x97SSC (0.75 M NaCl, 0.075M sodium pyrophosphate, 5xc3x97Denhardt""s solution, sonicated salmon sperm DNA (50 g/ml), 0.1% SDS, and 10% dextran sulfate at 42xc2x0 C., with washes at 42xc2x0 C. in 0.2xc3x97SSC and 0.1% SDS. Such hybridizable polynucleotide molecules would include genetically engineered or synthetic variants of the representative islet cell antigen polynucleotide sequence, SEQ ID NO: 1, and polynucleotide molecules that encode one or more amino acid substitutions, deletions or additions, preferably of a minor nature, as discussed above. Genetically engineered variants may be obtained by using oligonucleotide-directed site-specific mutagenesis, by use of restriction endonuclease digestion and adapter ligation, polymerase chain reaction (PCR), or other methods well established in the literature (see for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., 1989, and Smith et al., Genetic Engineering: Principles and Methods, Plenum Press, 1981; which are incorporated herein by reference). In addition, hybridizable polynucleotide molecules may encompass sequences containing degeneracies in the DNA code wherein host-preferred codons are substituted for the analogous codons in the representative sequences of SEQ ID NOs: 1, 15 and 21.
Analysis of the representative cDNA sequences of SEQ ID NO:1, 15 and 21 and their representative polypeptide sequences of SEQ ID NO:2, 16 and 22, show that they contain regions of homology to transmembrane protein tyrosine phosphatases. Comparison of the human protein tyrosine phosphatase IA-2/ICA512 cDNA and amino acid sequences with those of 1851 suggests that the coding region of macaque 1851 is missing amino-terminal sequence corresponding to approximately 1 amino acid and human 1851 is missing approximately 200 amino acid residues of the amino terminus. To recover the 5xe2x80x2 region, cDNA libraries from different tissues can be screened to obtain a full length cDNA, which encodes a full length mammalian islet cell antigen polypeptides. Another option for obtaining the complete coding sequence comprises using 5xe2x80x2 RACE (Rapid Amplification cDNA Ends) PCR. RACE is an art recognized PCR-based method for amplifying the 5xe2x80x2 ends of incomplete cDNAs, a frequent occurrence in cDNA cloning. To obtain the 5xe2x80x2 portion of a cDNA, PCR is carried out on specially prepared cDNA which contains unique anchor sequences, using anchor primers provided with the 5xe2x80x2 RACE reagents available from, for example, Clontech, Palo Alto, Calif. and a 3xe2x80x2 primer based on known sequence. The 5xe2x80x2-RACE-Ready cDNA can be purchased commercially (Clontech), or prepared according to known methods. A secondary PCR reaction can then be carried out using the anchor primer and a nested 3xe2x80x2 primer, according to known methods. Once a full-length cDNA is obtained, it is expressed and analyzed for overall structural similarity to known protein tyrosine phosphatases, and examined for features such as a continuous open reading frame flanked by translation initiation and termination sites and a potential signal sequence.
Transmembrane, or receptor-linked, protein tyrosine phosphatases consist of a conserved cytoplasmic domain which may have one or two (tandemly duplicated) catalytic regions, a single transmembrane domain, a highly variable extracellular domain and a signal peptide. These structural features suggest that receptor-linked protein tyrosine phosphatases would be capable of binding ligand and transducing external signal, but no ligands as of yet have been identified. Based on the representative amino acid sequence of SEQ ID NOs:2 and 15, the macaque 1851 polypeptide has an approximately 611 amino acid extracellular domain, from Ala, amino acid residue 1 to Lys, amino acid residue 611 of SEQ ID NO:16, containing a post translational modification dibasic site, at amino acid residue 423-424, or a tribasic site at amino acid residues 422-424; a 24 amino acid transmembrane domain comprising amino acid residue 241 to amino acid residue 265 of SEQ ID NO:2 or Phe, amino acid residue 612 to Cys, amino acid residue 635 of SEQ ID NO:16 and an approximately 375 amino acid cytoplasmic domain comprising the amino acid residue 265 to amino acid residue 640 of SEQ ID NO:2 or Leu, amino acid residue 636 to Gln, amino acid residue 1012 of SEQ ID NO:16. The representative amino acid sequence of the human islet cell antigen 1851 (SEQ ID NO:22) has 417 amino acids of an extracellular domain, from His, amino acid residue 1 to Lys, amino acid residue 417 of SEQ ID NO:22; a 24 amino acid residue transmembrane domain, from Phe, amino acid residue 418 to Cys, amino acid residue 441, of SEQ ID NO:22; and a 376 amino acid cytoplasmic domain, from Leu, amino acid residue 442 to Gln, amino acid residue 818 of SEQ ID NO:22.
The cytoplasmic domain of 1851 contains many regions that are conserved between members of the protein tyrosine phosphatase family. Within the cytoplasmic domain of protein tyrosine phosphatases is a catalytic region of about 230 amino acids, which contains a highly conserved catalytic core segment of approximately 11 amino acid residues (VHCXAGXXRXG SEQ ID NO:13) where the first three X""s are any amino acid, the fourth X is S or T, and the cysteine appears to be essential to the catalytic mechanism (Fischer et al., Science 253: 401-06). The catalytic core sequence of the representative macaque 1851 polypeptide sequences of SEQ ID Nos:2 and 16 and human 1851 polypeptide sequence represented by SEQ ID NO:22 differs from other members of the protein tyrosine phosphatase family in that alanine has been replaced by aspartic acid and the second variable amino acid (X) is alanine. 1851, like IA-2/ICA512, has a single catalytic region. Deletion of C-terminal amino acids from the intracellular domain of human islet cell antigen 1851 reduced reactivity with new onset IDDM sera, suggesting this region may play a role in defining an autoantibody epitope. Removal of the C-terminal 27 amino acids decreased reactivity from 19/53 sera (36%) to 10/53 sera (19%), a 47% decrease. Removal of the C-terminal 80 amino acids decreased reactivity further to 9/53 sera (17%), a 53% decrease, and removal of the C-terminal 160 amino acids abolished all recognition by all 53 new onset IDDM sera. This is similar to the reports of one of two described intracellular IA-2/ICA512 autoantibody epitopes (Bonifacio et al., J. Immunol. 155:5419-426, 1995). That human islet cell antigens 1851 and human IA-2/ICA512 are each precipitated by sera that do not precipitate the other suggests that each antigen has unique autoantibody epitopes, which is consistent with previous findings regarding the 37 kD and 40 kD tryptic fragments (Payton et al., J. Clin. Invest. 96:1506-11, 1995). A comparison between the overall human and macaque islet cell antigen 1851 nucleotide and amino acid sequences shows a 96.2% nucleotide identity and a 94.6% amino acid identity, in particular there was 97% identity within the nucleotide sequence and 98.9% identity within the amino acid sequence of the corresponding cytoplasmic domains, 100% identity within the transmembrane domain. There is 77% amino acid identity within the cytoplasmic domain between the claimed human (SEQ ID NO:22) and macaque (SEQ ID NO:16) islet cell antigen 1851 sequences and the reported human IA-2/ICA512 sequences (Lan et al., ibid.; and Rabin et al., ibid.). Between the full length macaque islet cell antigen 1851 sequence (as represented in SEQ ID Nos: 15 and 16) and rat phogrin sequences (Wasmeier and Hutton, J. Biol. Chem. 271:18161-70, 1996) there was less homology, 75.5% identity within the nucleotide sequence and 69.9% identity within the amino acid sequence.
In contrast, there is little homology in the extracellular regions of transmembrane protein tyrosine phosphatases. Some contain Ig-like and/or fibronectin type III repeats (Streuli et al., J. Exp. Med. 168: 1523, 1988; Hariharan et al., Proc. Natl. Acad. Aci. USA 88: 11266, 1991); others have glycosylated segments (Sap et al., Proc. Natl. Acad. Sci. USA 87:6112, 1990; and Krueger et al., EMBO J. 9: 3241, 1990) and a conserved cysteine-rich region (Tonks et al., J. Biol. Chem. 265: 10674-80, 1990) (Lan et al. ibid.). There is 31% identity between macaque islet cell antigen 1851 (as represented by SEQ ID NO:15) and IA-2/ICA512 (Lan et al., ibid.; and Rabin et al., ibid.) within the extracellular domain.
The tissue distribution of human islet cell antigen 1851 is generally neuroendocrine. Northern analysis showed strong hybridization to human mRNA from brain and pancreas and weaker hybridization in spinal cord, thyroid, adrenal and GI tract. In situ hybridization using macaque tissues further localized pancreatic and adrenal expression to islets and adrenal medulla, respectively. Northern blot analysis of rat phogrin showed expression in brain, pancreas and xcex1 and xcex2 cell tumor lines (Wasmeier and Hutton, ibid.); mouse IA-2xcex2 in brain, pancreas, stomach and in insulinoma and glucagomoma cell lines (Lu et al., Proc. Natl. Acad. Sci. USA 93:2307-11, 1996); human IA-2 in brain, pituitary and pancreas, four insulinoma cell lines and a glioblastoma cell line (Lan et al., ibid.); and human ICA512, brain and pancreas (Rabin et al., ibid.).
Limited trypsinization of IA-2/ICA512 and human islet cell antigen 1851 yielded a 40 kD IA-2/ICA512 fragment and a 37 kD islet cell antigen 1851 fragment. These correspond to the 37 kD and 40 kD tryptic fragments described by Christie et al. (J. Exp. Med. 172:789-94, 1990), Payton et al. (J. Clin. Invest. 96:1506-11, 1995), Bonifacio et al. (J. Immunol. 155:5419-26, 1995), Lu et al. (Proc. Natl. Acad. Sci. USA 93:2307-11, 1996) and Wasmeier and Hutton (ibid.).
Members of the protein tyrosine phosphatase family have been shown to display alternative mRNA splicing (Moeller et al., WO 94/21800; Hall et al., J. Immunol. 141: 2781-87, 1988; Johnson et al., J. Biol. Chem. 264: 6220-29, 1989; Streuli and Saito, EMBO J. 8: 787-96, 1989; Matthews et al., Proc. Natl. Acad. Sci. USA 87: 4444-48, 1990; Walton and Dixon, Ann. Rev. Biochem. 62: 101-20, 1993; and Pan et al., J. Biol. Chem. 268: 19284-91, 1993). Alternative splicing may be important in autoantibody recognition; xe2x80x9cinappropriatexe2x80x9d splicing could lead to autoimmunity by activating T cells, for example.
The invention provides isolated DNA molecules that are useful in producing recombinant islet cell antigens. As will be evident to one skilled in the art, each individual domain or combinations of the domains may be prepared synthetically or by recombinant DNA techniques for use in the present invention. Thus, the present invention provides the advantage that islet cell antigens are produced in high quantities that may be readily purified using methods known in the art (see generally; Scopes, Protein Purification, Springer-Verlag, N.Y., 1982). Alternatively, the proteins of the present invention may be synthesized following conventional synthesis methods, such as the solid-phase synthesis method of Barany and Merrifield (in The Peptides. Analysis, Synthesis, Biology Vol. 2, Gross and Meienhofer, eds, Academic Press, NY, pp. 1-284, 1980), by partial solid-phase techniques, by fragment condensation or by classical solution addition.
DNA molecules of the present invention can be isolated using standard cloning methods such as those described by Maniatis et al. (Molecular Cloning: A Laboratory Manual, Cold Spring Harbor, N.Y., 1982; which is incorporated herein by reference), Sambrook et al., (Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., 1989), or Mullis et al. (U.S. Pat. No. 4,683,195) which are incorporated herein by reference. Alternatively, the coding sequences of the present invention can be synthesized using standard techniques that are well known in the art, such as by synthesis on an automated DNA synthesizer.
The sequence of a polynucleotide molecule encoding a representative islet cell antigen polypeptide is shown in SEQ ID NOs: 1, 15 and 21 and the corresponding amino acid sequences are shown in SEQ ID NOs: 2, 16 and 22. Those skilled in the art will recognize that these sequences correspond to one allele of either the macaque or human gene, and that allelic variation is expected to exist. Allelic variants of the DNA sequence shown in SEQ ID NO: 1, 15 and 21 including those containing silent mutations and those in which mutations result in amino acid sequence changes, are within the scope of the present invention, as are proteins which are allelic variants of SEQ ID NO: 2, 16 and 22.
The macaque sequence disclosed herein is useful for isolating polynucleotide molecules encoding islet cell antigen polypeptides from other species (xe2x80x9cspecies homologsxe2x80x9d). In particular, the macaque cDNA was used to conduct a sequence search for a human homolog. A match was found as an expressed sequence tag (EST) from a human fetal brain library submitted to the Genbank database (GenBank ID: TO361, clone ID: HFBCV88). This 127 amino acid polypeptide, SEQ ID NO:5, had homology to a region of the cytoplasmic domain of M1.18.5.1 (SEQ ID NO:2) and was used to design PCR primers to clone a 1.1 kD cytoplasmic portion (SEQ ID NOs:6 and 7) of the human 1851 sequence, as described in the examples below. Other preferred species homologs include mammalian homologs such as bovine, canine, porcine, ovine, and equine proteins. Methods for using sequence information from a first species to clone a corresponding polynucleotide sequence from a second species are well known in the art. See, for example, Ausubel et al., eds., Current Protocols in Molecular Biology, John Wiley and Sons, Inc., NY, 1987.
DNA molecules of the present invention or portions thereof may be used as probes, for example, to directly detect 1851 sequences in cells or biological samples. Such DNA molecules are generally synthetic oligonucleotides, but may be generated from cloned cDNA or genomic sequences and will generally comprise at least about 16 nucleotides, more often from about 17 nucleotides to about 25 or more nucleotides, sometimes 40 to 60 nucleotides, and in some instances a substantial portion or even the entire 1851 gene or cDNA. The synthetic oligonucleotides of the present invention have at least 85% identity to a representative macaque or human 1851 DNA sequence (SEQ ID Nos:1, 15 and 21) or their complements. For use as probes, the molecules are labeled to provide a detectable signal, such as with an enzyme, biotin, a radionuclide, fluorophore, chemiluminescer, paramagnetic particle, etc., according to methods known in the art. Probes of the present invention may also be used in diagnostic methods to detect autoantibodies in diabetic and prediabetic sera.
DNA molecules used within the present invention may be labeled and used in a hybridization procedure similar to the Southern or dot blot. As will be understood by those skilled in the art, conditions that allow the DNA molecules of the present invention to hybridize to the representative DNA sequence of SEQ ID NO:1, 15 or 21 or their allelic variants may be determined by methods well known in the art (reviewed, for example, by Sambrook et al. Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., 1989; which is incorporated herein by reference). Those skilled in the art will be capable of varying hybridization conditions (i.e. stringency of hybridization) of the DNA molecules as appropriate for use in the various procedures by methods well known in the literature (see, for example, Sambrook et al., ibid., pages 11.45-11.53). The higher the stringency of hybridization, the lower the number of mismatched sequences detected. Alternatively, lower stringency will allow related sequences to be identified.
Alternatively, allelic variants may be identified using DNA molecules of the present invention and, for example, the polymerase chain reaction (PCR) (disclosed by Saiki et al., Science 239: 487, 1987; Mullis et al., U.S. Pat. No. 4,686,195; and Mullis et al., U.S. Pat. No. 4,683,202) to amplify DNA sequences, which are subsequently detected by their characteristic size on agarose gels or which may be sequenced to detect sequence abnormalities.
DNA molecules encoding the islet cell antigen polypeptides of the present invention may be inserted into DNA constructs. As used within the context of the present invention a DNA construct is understood to refer to a DNA molecule, or a clone of such a molecule, either single- or double-stranded, which has been modified through human intervention to contain segments of DNA combined and juxtaposed in a manner that would not otherwise exist in nature. DNA constructs of the present invention comprise a first DNA segment encoding an islet cell antigen polypeptide operably linked to additional DNA segments required for the expression of the first DNA segment. Within the context of the present invention, additional DNA segments will generally include promoters and transcription terminators, and may further include enhancers and other elements. One or more selectable markers may also be included. DNA constructs useful for expressing cloned DNA segments in a variety of prokaryotic and eukaryotic host cells can be prepared from readily available components or purchase from commercial suppliers.
In general, a DNA sequence encoding a protein of the present invention is operably linked to a transcription promoter and terminator within a DNA construct. The construct will commonly contain one or more selectable markers and one or more origins of replication, although those skilled in the art will recognize that within certain systems selectable markers may be provided on separate vectors, and replication of the exogenous DNA may be provided by integration into the host cell genome. Selection of promoters, terminators, selectable markers, vectors and other elements is a matter of routine design within the level of ordinary skill in the art. Many such elements are described in the literature and are available through commercial suppliers.
In one embodiment the first DNA segment is an isolated polynucleotide molecule encoding a mammalian islet cell antigen polypeptide comprising the amino acid sequence of SEQ ID NO:4, wherein the polypeptide forms an immune complex with autoantibodies from a patient at risk of or predisposed to IDDM. In another embodiment, the first DNA segment is an isolated polynucleotide encoding a polypeptide of SEQ ID NO:2 from Leu, amino acid residue 265 to Gln, amino acid residue 641. In another embodiment, the first DNA segment is an isolated polynucleotide encoding a polypeptide of SEQ ID NO:2 from Ser, amino acid residue 1, to Gln, amino acid residue 641.
Within yet another embodiment, the first DNA segment is an isolated polynucleotide encoding a polypeptide of SEQ ID NO:22 from Leu, amino acid residue 442 to Gln, amino acid residue 818. In another embodiment, the first DNA segment is an isolated polynucleotide encoding a polypeptide of SEQ ID NO:16 from Ala, amino acid residue 1 to Gln, amino acid residue 1012.
The proteins of the present invention can be produced in genetically engineered host cells according to conventional techniques. Suitable host cells are those cell types that can be transformed or transfected with exogenous DNA and grown in culture, and include bacteria, fungal cells, and cultured higher eukaryotic cells. Techniques for manipulating cloned DNA molecules and introducing exogenous DNA into a variety of host cells are disclosed by Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989, and Ausubel et al., ibid., which are incorporated herein by reference.
To direct a protein of the present invention into the secretory pathway of the host cells, a secretory signal sequence (also known as a leader sequence, prepro sequence or pre sequence) is provided in the expression vector. The secretory signal sequence is joined to the DNA sequence encoding a protein of the present invention in the correct reading frame. Secretory signal sequences are commonly positioned 5xe2x80x2 to the DNA sequence encoding the protein of interest, although certain signal sequences may be positioned elsewhere in the DNA sequence of interest (see, e.g., Welch et al., U.S. Pat. No. 5,037,743; Holland et al., U.S. Pat. No. 5,143,830). The secretory signal sequence may be that normally associated with a protein of the present invention, or may be from a gene encoding another secreted protein.
Cultured mammalian cells are also preferred hosts within the present invention. A preferred vector system for use in the present invention is the pZCEP vector system as disclosed by Jelineck et al., Science, 259: 1615-16, 1993. Methods for introducing exogenous DNA into mammalian host cells include calcium phosphate-mediated transfection (Wigler et al., Cell 14:725, 1978; Corsaro and Pearson, Somatic Cell Genetics 7:603, 1981: Graham and Van der Eb, Virology 52:456, 1973), electroporation (Neumann et al., EMBO J. 1:841-845, 1982), DEAE-dextran mediated transfection (Ausubel et al., eds., Current Protocols in Molecular Biology, John Wiley and Sons, Inc., NY, 1987), and cationic lipid transfection using commercially available reagents including the Boehringer Mannheim Transfection-Reagent (N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethyl ammoniummethylsulfate; Boehringer Mannheim, Indianapolis, Ind.) or LIPOFECTINxcx9creagent (N-[1-(2,3-Dioleyloxy)propyl]-N,N,N-trimethylammonium chloride and dioeleoyl phosphatidylethanolamine; GIBCO-BRL, Gaithersburg, Md.) using the manufacturer-supplied directions, which are incorporated herein by reference. The production of recombinant proteins in cultured mammalian cells is disclosed, for example, by Levinson et al., U.S. Pat. No. 4,713,339; Hagen et al., U.S. Pat. No. 4,784,950; Palmiter et al., U.S. Pat. No. 4,579,821; and Ringold, U.S. Pat. No. 4,656,134, which are incorporated herein by reference. Preferred cultured mammalian cells include the COS-1 (ATCC No. CRL 1650), COS-7 (ATCC No. CRL 1651), BHK (ATCC No. CRL 1632), BHK 570 (ATCC No. CRL 10314), 293 (ATCC No. CRL 1573; Graham et al., J. Gen. Virol. 36:59-72, 1977) and Chinese hamster ovary (e.g. CHO-K1; ATCC No. CCL 61) cell lines. Additional suitable cell lines are known in the art and available from public depositories such as the American Type Culture Collection, Rockville, Md. In general, strong transcription promoters are preferred, such as promoters from SV-40 or cytomegalovirus.
Prokaryotic cells can also serve as host cells for use in carrying out the present invention. Particularly preferred are strains of the bacteria Escherichia coli, although Bacillus and other genera are also useful. Techniques for transforming these hosts and expressing foreign DNA sequences cloned therein are well known in the art (see, e.g., Sambrook et al., ibid.). When expressing the proteins in bacteria such as E. coli, the protein may be retained in the cytoplasm, typically as insoluble granules, or may be directed to the periplasmic space. In the former case, the cells are lysed, and the granules are recovered and denatured using, for example, guanidine isothiocyanate. The denatured protein is then refolded by diluting the denaturant. In the latter case, the protein can be recovered from the periplasmic space in a soluble form.
Fungal cells are also suitable as host cells. For example, Saccharomyces ssp., Hansenula polymorpha, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces fragilis, Ustilago maydis, Pichia pastoris, Pichia guillermondii, Pichia methanolica, and Candida maltosa transformation systems are known in the art. See, for example, Kawasaki, U.S. Pat. No. 4,599,311, Kawasaki et al., U.S. Pat. No. 4,931,373, Brake, U.S. Pat. No. 4,870,008; Welch et al., U.S. Pat. No. 5,037,743; and Murray et al., U.S. Pat. No. 4,845,075, Gleeson et al., J. Gen. Microbiol. 132:3459-3465, 1986 and Cregg, U.S. Pat. No. 4,882,279. Aspergillus cells may be utilized according to the methods of McKnight et al., U.S. Pat. No. 4,935,349, which is incorporated herein by reference. Methods for transforming Acremonium chrysogenum are disclosed by Sumino et al., U.S. Pat. No. 5,162,228, which is incorporated herein by reference.
Other higher eukaryotic cells can also be used as hosts, including insect cells, plant cells and avian cells. Transformation of insect cells and production of foreign proteins therein is disclosed by Guarino et al., U.S. Pat. No. 5,162,222 and Bang et al., U.S. Pat. No. 4,775,624, which are incorporated herein by reference. The use of Agrobacterium rhizogenes as a vector for expressing genes in plant cells has been reviewed by Sinkar et al., J. Biosci. (Bangalore) 11:47-58, 1987.
Drug selection is generally used to select for cultured mammalian cells into which foreign DNA has been inserted. Such cells are commonly referred to as xe2x80x9ctransfectantsxe2x80x9d. Cells that have been cultured in the presence of the selective agent and are able to pass the gene of interest to their progeny are referred to as xe2x80x9cstable transfectants.xe2x80x9d A preferred selectable marker is a gene encoding resistance to the antibiotic neomycin. Selection is carried out in the presence of a neomycin-type drug, such as G-418 or the like. Selection systems may also be used to increase the expression level of the gene of interest, a process referred to as xe2x80x9camplification.xe2x80x9d Amplification is carried out by culturing transfectants in the presence of a low level of the selective agent and then increasing the amount of selective agent to select for cells that produce high levels of the products of the introduced genes. A preferred amplifiable selectable marker is dihydrofolate reductase, which confers resistance to methotrexate.
Transformed or transfected host cells are cultured according to conventional procedures in a culture medium containing nutrients and other components required for the growth of the chosen host cells. A variety of suitable media, including defined media and complex media, are known in the art and generally include a carbon source, a nitrogen source, essential amino acids, vitamins and minerals. Media may also contain such components as growth factors or serum, as required. The growth medium will generally select for cells containing the exogenously added DNA by, for example, drug selection or deficiency in an essential nutrient which is complemented by the selectable marker carried on the expression vector or co-transfected into the host cell.
The recombinant islet cell antigen polypeptides expressed using the methods described herein are isolated and purified by conventional procedures, including separating the cells from the medium by centrifugation or filtration, precipitating the proteinaceous components of the supernatant or filtrate by means of a salt, e.g. ammonium sulfate, purification by a variety of chromatographic procedures, e.g. ion exchange chromatography or affinity chromatography, or the like. Methods of protein purification are known in the art (see generally, Scopes, R., Protein Purification, Springer-Verlag, N.Y. (1982), which is incorporated herein by reference) and may be applied to the purification of the recombinant proteins of the present invention. Substantially pure recombinant islet cell antigen polypeptides of at least about 50% is preferred, at least about 70-80% more preferred, and 95-99% or more homogeneity most preferred, particularly for pharmaceutical uses. Once purified, partially or to homogeneity, as desired, the recombinant islet cell antigen polypeptides may then be used diagnostically, therapeutically, etc. as further described below.
Recombinant 1851 polypeptides can also be produced by expressing islet cell antigen DNA fragments, such as fragments generated by digesting an islet cell antigen cDNA at convenient restriction sites. The isolated recombinant polypeptides or cell-conditioned media are then assayed for activity as described in the examples below. Alternatively, the proteins of the present invention may be synthesized following conventional synthesis methods such as the solid-phase synthesis using the method of Barany and Merrifield (in The Peptides. Analysis, Synthesis, Biology Vol. 2, Gross and Meienhofer, eds, Academic Press, NY, pp. 1-284, 1980, which are incorporated herein by reference), by partial solid-phase techniques, by fragment condensation or by classical solution addition. Short polypeptide sequences, or libraries of overlapping peptides, usually from about 6 up to about 35 amino acids, which correspond to selected islet cell antigen polypeptide regions can be readily synthesized and then screened in screening assays designed to identify peptides having a desired activity, such as domains which are responsible for or contribute to binding activity, immunodominant epitopes (particularly those recognized by autoantibodies), and the like.
Although the use of recombinant 1851 polypeptides is preferred within the methods of the present invention, 1851 polypeptides may also be prepared from cells that naturally produce 1851 protein (such as islet cells). For example, 1851 polypeptides may be prepared from islet cells by isolation of a membrane fraction. This 1851-enriched fraction is then used to detect autoantibodies to 1851 in prediabetic and diabetic sera.
Islet cell antigen polypeptides produced according to the present invention can be used diagnostically, in the detection and quantitation of autoantibodies in a biological sample, that is, any sample derived from or containing cells, cell components or cell products, including, but not limited to, cell culture supernatants, cell lysates, cleared cell lysates, cell extracts, tissue extracts, blood plasma, serum, and fractions thereof. By means of having islet cell antigen polypeptides which specifically bind to autoantibodies in prediabetic and diabetic sera, the presence or absence of such autoantibodies can be determined, and the concentration of such autoantibodies in an individual can be measured. This information can then be used to monitor the progression or regression of the potentially harmful autoantibodies in individuals at risk of, or with a predisposition to develop IDDM, and would be useful for predicting the clinical course of the disease in a patient. The assay results can also find use in monitoring the effectiveness of therapeutic measures for treatment of IDDM or related diseases.
As will be recognized by those skilled in the art, numerous types of immunoassays are available for use in determining the presence of autoantibodies. For instance, direct and indirect binding assays, competitive assays, sandwich assays, and the like, as are generally described in, e.g., U.S. Pat. Nos. 4,642,285; 4,376,110; 4,016,043; 3,879,262; 3,852,157; 3,850,752; 3,839,153; 3,791,932; and Harlow and Lane, Antibodies, A Laboratory Manual, Cold Spring Harbor Publications, N.Y., 1988, each incorporated herein by reference. In one assay format, autoantibodies directed to the polypeptides of the present invention are quantified directly by measuring the binding of autoantibodies in a biological sample to recombinant or synthetic islet cell antigen polypeptides. The biological sample is contacted with at least one islet cell antigen polypeptide of the invention under conditions conducive to immune complex formation. The immune complexes formed between the islet cell antigen polypeptide and the antibodies are then detected, and the presence and quantity of autoantibodies can then be used to diagnose or direct treatment of IDDM. The immune complexes can be detected by means of antibodies that bind to the islet cell antigen of the present invention or by labeling the polypeptide as described below. Separation steps (e.g., washes) may be necessary in some cases to distinguish specific binding over background. In another format, the serum level of a patient""s autoantibodies to the islet cell antigen polypeptides in serum can be measured by competitive binding with labeled or unlabeled antibodies to the islet cell antigen polypeptides of the present invention. Unlabeled 1851 polypeptides can be used in combination with labeled antibodies that bind to human antibodies or to islet cell antigens. Alternatively, the islet cell antigen polypeptide can be directly labeled. A wide variety of labels can be employed, such as radionuclides, particles (e.g., gold, ferritin, magnetic particles, red blood cells), fluors, enzymes, enzyme substrates, enzyme cofactors, enzyme inhibitors, ligands (particularly haptens), chemiluminescers, biotin and other compounds that provide for the detection of the labeled polypeptide or protein. For example, an 1851 polypeptide can be radiolabeled using conventional methods such as in vitro transcription and translation. Radiolabeled 1851 polypeptide is combined with patient serum under conditions suitable for immune complex formation. Immune complexes are then separated, such as by binding to protein A. Precipitated 1851 polypeptides are then quantitated by conventional methods, such as gel electrophoresis, fluorography, densitometry or by direct counting of immunoprecipitated, radiolabeled antigen. The amount of 1851 polypeptide precipitated by test sera can be statistically compared to mean counts precipitated by healthy control sera, each measured separately. In an alternative format, an 1851 polypeptide antigen, labeled with biotin, is combined with patient serum under conditions suitable for immune complex formation. The serum is then transferred to a protein A-coated container, such as a well of an assay plate, and the container is allowed to stand so that immune complexes can form. The container is then washed, and streptavidin, conjugated to a suitable enzyme (e.g. alkaline phosphatase), is added. A chromogenic substrate is then added, and the presence of 1851 polypeptide autoantibodies in the sample is indicated by a color change. Additional assay formats will be evident to those skilled in the art.
Thus, autoantibodies to islet cell antigen polypeptides can be identified and, if desired, extracted from a patient""s serum by binding to 1851 polypeptides of the present invention. The islet cell antigen polypeptides may be attached, e.g., by adsorption, to an insoluble or solid support, such as ELISA microtiter well, microbead, filter membrane, insoluble or precipitable soluble polymer, etc. to function as an affinity resin. The captured autoantibodies can then be identified by several methods. For example, antisera or monoclonal antibodies to the antibodies can be used. These antisera or monoclonal antibodies are typically non-human in origin, such as rabbit, goat, mouse, etc. These anti-antibodies can be detected directly if attached to a label such as 125I, enzyme, biotin, etc., or can be detected indirectly by a labeled secondary antibody made to specifically detect the anti-antibody.
The diagnostic methods of the present invention can be used in conjunction with other known assays and diagnostic techniques (see for example, WO 95/07464, incorporated herein by reference in its entirety). Such other assays and techniques include measurement of body mass index (BMI), defined as the quotient of the patient""s weight in kg divided by the square of height in meters; C-peptide level (Heding, Diabetoloqia 11: 541-548 (1975); Landin-Olsson et al., Diabetoloqia 33: 561-568 (1990)); or one or more additional diabetes-associated autoantibodies, genotypes or loci. A low BMI (i.e. less than about 25) in combination with other indicators is suggestive of type I diabetes. BMI is thus a useful indicator for distinguishing type I from type II diabetes. C-peptide level can be measured using standard methods, such as that of Heding (ibid.), in which insulin and proinsulin are removed from serum and C-peptide is measured in the resulting insulin-free fraction radioimmunologically.
The islet cell antigen polypeptides of the current invention can also be used to assess T cell reactivity, as a method for monitoring the disease state in a patient. Mammalian islet cell antigen 1851 peptides will generally comprise at least about 12 amino acids, and more often from about 15 amino acids to about 20 or more amino acids. In some instances, a substantial portion or domain or even the entire 1851 protein, can be used to assess T cell reactivity in peripheral blood mononuclear cells (PBMNCs) from prediabetics. Methods for detecting such in vitro activity are known in the art, including a proliferation assay measuring 3H-thymidine incorporation, analysis of activation markers, such as CD69, or measuring cytokine production, such as IL-2. Correlations can be drawn between T cell reactivity to islet cell antigen 1851 and conversion from prediabetes to diabetes. This correlation would be consistent with the appearance of autoantibodies to islet cell antigen peptides late in prediabetes (Christie et al., Diabetes 43:1254-59, 1994).
Mammalian cells, such as COS cells or L cells, may also be transfected with appropriate Class I or Class II alleles specific for the islet cell antigen of the present invention. Such MHC molecules may be soluble or membrane bound, and the 1851 antigenic polypeptide may be recombinantly tethered to the N-terminal region of the xcex1 or xcex2 chain using a flexible linker containing, for example, repeating glycine residues separated by a serine residue, such that the antigenic peptide binds to the MHC molecule and is properly presented to the T cell. Alternatively, the antigenic peptide may be exogenously loaded into the MHC peptide binding grove. The MHC-antigenic peptide complex can then be used to assess the reactivity of peripheral blood T cells derived from prediabetic or diabetic patients. This reactivity may be assessed by methods known in the art, such as 3H thymidine incorporation, cytokine production or cytolysis. Alternatively, islet cell antigen expressed in microorganisms can be xe2x80x9cfedxe2x80x9d to peripheral blood mononuclear cells (PBMN). The antigen-fed cells can then be used to stimulate peripheral blood T cells derived from diabetics or prediabetics.
The islet cell antigen polypeptides are also contemplated to be advantageous for use as immunotherapeutics to induce immunological tolerance or nonresponsiveness (anergy) to 1851 polypeptide autoantigens in patients predisposed or already mounting an immune response to 1851 polypeptide autoantigens of the islet xcex2-cells. This therapy can take the form of autoantigenic 1851 peptides bound to an appropriate MHC Class I or Class II molecule as described above. The therapy can also be in the form of oral tolerance (Weiner et al., Nature 376: 177-80, 1995), or IV tolerance, for example. The use of polypeptide antigens in suppression of autoimmune disease is disclosed by Wraith, et al., (Cell 59: 247-55, 1989). Tolerance can be induced in patients, although conditions for inducing such tolerance will vary according to a variety of factors. In a neonate, tolerance can be induced by parenteral injection of an islet cell antigenic polypeptide, either with recombinant polypeptide or synthetic antigen, or more conveniently by oral administration in an appropriate formulation. The precise amount of administration, its mode and frequency of dosages will vary.
To induce immunological tolerance to the islet cell autoantigens in an adult susceptible to or already suffering from a islet cell antigen related disease such as IDDM, the precise amounts and frequency of administration will also vary, for adults about 1 to 1,000 mg/kg can be administered by a variety of routes, such as parenterally, orally, by aerosols, intradermal injection, etc. For neonates the doses will generally be higher than those administered to adults; e.g. 100 to 1,000 mg/kg.
The islet cell antigen 1851 polypeptides will typically be more tolerogenic when administered in a soluble form rather than an aggregrated or particulate form. Persistence of an islet cell antigen polypeptide of the invention is generally needed to maintain tolerance in an adult, and thus may require more frequent administration of the antigen, or its administration in a form which extends the half-life of the islet cell antigen. See for example, Sun et al. (Proc. Natl. Acad. Sci. USA 91: 10795-99, 1994).
The islet cell antigen polypeptides described herein are also contemplated to be advantageous for use as immunotherapeutics in treating longer term IDDM patients that have been identified by autoantibody testing at the time of clinical non-insulin dependent diabetes mellitus (NIDDM) diagnosis. Intervention in these patients may be especially effective, perhaps due to the slowly progressive nature of their xcex2 cell destruction. Since the numbers of such patients is nearly the same as those with classical childhood IDDM, there is a need for such therapeutic intervention (Hagopian et al., J. Clin. Invest. 91:368-74; 1993; Harris and Robbins, Diabetes Care 17:1337-40, 1994; and Kobayashi et al., Diabetes 45:622-26, 1996).
The N-terminal domain of islet cell antigen 1851 is expected to be inside the insulin secretory granule. The islet cell antigen polypeptides of the current invention contain post translational modification sites within the N-terminal domain. A dibasic site or tribasic site at amino acid residues 228-230 (Arg-Lys-Lys) in SEQ ID NO:22 and amino acid residues 422-424 (Arg-Lys-Lys) in SEQ ID NO:16 could result in cleavage of a 420 amino acid post-translationally modified mammalian islet cell antigen polypeptide from the islet cell antigen 1851 polypeptide. All or part of this cleaved polypeptide may be released from the xcex2 cell via either the constitutive secretory pathway for granule halo components, or via the regulated pathway involved in insulin release. Detection and quantitation of post translationally modified polypeptides in a biological sample (that is, any sample derived from or containing cells, cell components or cell products, including, but not limited to, cell culture supernatants, cell lysates, cleared cell lysates, cell extracts, tissue extracts, blood plasma, serum, and fractions thereof) can be used diagnostically to monitor disease state in a patient. The presence or absence of such polypeptides in prediabetic and diabetic sera can be determined, for example by radioimmunoassay, and the concentration of such polypeptides in such an individual serum sample can be measured. This information can then be used, for example, to monitor insulin secretory activity, such as xcex2 cell insulin secretory rates; or to indicate altered xcex2 cell physiology associated with cellular stress as in an immune attack. Peptide levels could be an indicator of xcex2 cell distress or xcex2 cell death, and would be useful for predicting the disease state in a patient. Alternatively, the peptides herein function serve in paracrine or endocrine signaling to other islet cells or remote cells in other organs. The assay results can also find use in monitoring the effectiveness of therapeutic measures for treatment of IDDM or related diseases. In a preferred embodiment, a post-translationally modified mammalian islet cell antigen polypeptide comprises the sequence of SEQ ID NO:22 from His, amino acid residue 1 to Glu, amino acid residue 227. In another preferred embodiment the biological sample is blood.
The present invention also relates to a pharmaceutical composition comprising an islet cell antigen polypeptide of the present invention, together with a pharmaceutically acceptable carrier or vehicle, such as saline, buffered saline, water or the like. Formulations may further include one or more excipients, preservatives, solubilizers, etc. Methods of formulation are well known in the art and are disclosed, for example, in Remington""s Pharmaceutical Sciences, Gennaro, ed., Mack Publishing Co., Easton Pa., 1990, which is incorporated herein by reference. Therapeutic doses will generally be in the range of 0.1 to 100 xcexcg/kg of patient weight, with the exact dose determined by the clinician according to accepted standards, taking into account the nature and severity of the condition to be treated, patient traits, etc. Determination of dose is within the level of ordinary skill in the art. In general, a therapeutically effective amount of an islet cell antigen polypeptide of the present invention is an amount sufficient to produce a clinically significant reduction in xcex2-cell loss or a delay of clinical onset of IDDM.
In a related aspect, the present invention provides diagnostic kits for use with the recombinant or synthetic islet cell antigen polypeptides of the present invention, in detecting autoantibodies to pancreatic xcex2-islet cells. Thus, 1851 polypeptides may be provided, usually in lyophilized form, in a container, either alone or in conjunction with additional reagents, such as 1851-specific antibodies, labels, and/or anti-human antibodies and the like. The 1851 polypeptides and antibodies, which may be conjugated to a label or unconjugated, are included in the kits with buffers, such as Tris phosphate, carbonate, etc., stabilizers, biocides, inert proteins, e.g., serum albumin, and the like. Frequently it will be desirable to include an inert extender or excipient to dilute the active ingredients, where the excipient may be present in from about 1 to 99% of the total composition. Where an antibody capable of binding to the islet cell antigen polypeptide autoantibody or to the recombinant or synthetic 1851 polypeptide is employed in an assay, this will typically be present in a separate vial.
Within one aspect of the present invention, islet cell antigen polypeptides, including derivatives thereof, as well as portions or fragments of these polypeptides, are utilized to prepare antibodies for diagnostic or therapeutic uses which specifically bind to islet cell antigen polypeptides. As used herein, the term xe2x80x9cantibodiesxe2x80x9d includes polyclonal antibodies, monoclonal antibodies, antigen-binding fragments thereof such as F(abxe2x80x2)2 and Fab fragments, as well as recombinantly produced binding partners. These binding partners incorporate the variable regions from a gene which encodes a specifically binding monoclonal antibody. Antibodies are defined to be specifically binding if they bind to the islet cell antigen polypeptides with a Ka of greater than or equal to 107/M. The affinity of a monoclonal antibody or binding partner may be readily determined by one of ordinary skill in the art (see, Scatchard, Ann. NY Acad. Sci. 51: 660-72, 1949).
Methods for preparing polyclonal and monoclonal antibodies have been well described in the literature (see for example, Sambrook et al., Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor, N.Y., 1989; and Hurrell, J. G. R., Ed., Monoclonal Hybridoma Antibodies: Techniques and Applications, CRC Press, Inc., Boca Raton, Fla., 1982, which is incorporated herein by reference). As would be evident to one of ordinary skill in the art, polyclonal antibodies may be generated from a variety of warm-blooded animals such as horses, cows, goats, sheep, dogs, chickens, rabbits, mice, or rats, for example. The immunogenicity of the islet cell antigen polypeptide may be increased through the use of an adjuvant such as Freund""s complete or incomplete adjuvant. A variety of assays known to those skilled in the art may be utilized to detect antibodies which specifically bind to an islet cell antigen. Exemplary assays are described in detail in Antibodies: A Laboratory Manual, Harlow and Lane (Eds.), Cold Spring Harbor Laboratory Press, 1988. Representative examples of such assays include: concurrent immunoelectrophoresis, radio-immunoassays, radio-immunoprecipitations, enzyme-linked immuno-sorbent assays, dot blot assays, inhibition or competition assays, and sandwich assays.
Additional techniques for the preparation of monoclonal antibodies may be utilized to construct and express recombinant monoclonal antibodies. Briefly, mRNA is isolated from a xcex2 cell population and used to create heavy and light chain immunoglobulin cDNA expression libraries in a suitable vector such as the xcexIMMUNOZAP(H) and xcexIMMUNOZAP(L) vectors, which may be obtained from Stratogene Cloning Systems (La Jolla, Calif.). These vectors are then screened individually or are co-expressed to form Fab fragments or antibodies (Huse et al., Science 246: 1275-81, 1989; Sastry et al., Proc. Natl. Acad. Sci. USA 86: 5728-32, 1989). Positive plaques are subsequently converted to a non-lytic plasmid which allows high level expression of monoclonal antibody fragments in E. coli. 
Binding partners such as those described above may also be constructed utilizing recombinant DNA techniques to incorporate the variable regions of a gene which encodes a specifically binding antibody. The construction of these proteins may be readily accomplished by one of ordinary skill in the art (see for example, Larrick et al., Biotechnology 7: 934-38, 1989; Reichmann et al., Nature 322: 323-27, 1988 and Roberts et al. Nature 328: 731-34, 1987). Once suitable antibodies or binding partners have been obtained, they may be isolated or purified by many techniques well described in the literature (see for example, Antibodies: A Laboratory Manual, ibid.). Suitable techniques include protein or peptide affinity columns, HPLC or RP-HPLC, purification on protein A or protein G columns or any combination of these techniques. Within the context of the present invention, the term xe2x80x9cisolatedxe2x80x9d as used to define antibodies or binding partners means xe2x80x9csubstantially free of other blood components.xe2x80x9d
Antibodies of the present invention may be produced by immunizing an animal, a wide variety of warm-blooded animals such as horses, cows, goats, sheep, dogs, chickens, rabbits, mice, and rats can be used, with a recombinant or synthetic islet cell antigen polypeptide or a selected portion thereof (e.g., a peptide). For example, by selected screening one can identify a region of the islet cell antigen polypeptide such as that predominantly responsible for recognition by anti-islet cell antigen polypeptide antibodies, or a portion which comprises an epitope of a islet cell antigen polypeptide variable region, which may thus serve as a islet cell antigen polypeptide-specific marker. Antibody producing cells obtained from the immunized animals are immortalized and screened, or screened first for, e.g., the production of antibody which inhibits the interaction of the anti-islet cell antigen polypeptide autoantibody with the islet cell antigen polypeptide and then immortalized. As the generation of human monoclonal antibodies to a human antigen, such as an 1851 polypeptide, may be difficult with conventional immortalization techniques, it may be desirable to first make non-human antibodies and then transfer via recombinant DNA techniques the antigen binding regions of the non-human antibodies, e.g. the F(abxe2x80x2)2 or hypervariable regions, to human constant regions (Fc) or framework regions to produce substantially human molecules. Such methods are generally known in the art and are described in, for example, U.S. Pat. No. 4,816,397, and EP publications 173,494 and 239,400, which are incorporated herein by reference.
Alternatively, one may isolate DNA sequences which encode a human monoclonal antibody or portions thereof that specifically bind to islet cell antigen polypeptides by screening a DNA library from human B cells according to the general protocol outlined by Huse et al., Science 246: 1275-81, 1989, incorporated herein by reference, and then cloning and amplifying the sequences which encode the antibody (or binding fragment) of the desired specificity.
In another aspect of the invention, the mammalian islet cell antigen polypeptides can be used to clone T cells which have specific receptors for the islet cell antigen polypeptide. Once the islet cell antigen polypeptide specific T cells are isolated and cloned using techniques generally available to the skilled artisan, the T cells or membrane preparations thereof can be used to immunize animals to produce antibodies to the islet cell antigen polypeptide receptors on T cells. The antibodies can be polyclonal or monoclonal. If polyclonal, the antibodies can be murine, lagomorph, equine, ovine, or from a variety of other mammals. Monoclonal antibodies will typically be murine in origin, produced according to known techniques, or human, as described above, or combinations thereof, as in chimeric or humanized antibodies. The anti-islet cell antigen polypeptide receptor antibodies thus obtained can then be administered to patients to reduce or eliminate T cell subpopulations which recognize and participate in the immunological destruction of islet cell antigen polypeptide bearing cells in an individual predisposed to or already suffering from a disease, such as IDDM. Further, the islet cell antigen polypeptide T cell receptors can thus be identified, cloned and sequenced, and receptor polypeptides synthesized which bind to the islet cell antigen polypeptides and block recognition of the islet cell antigen polypeptide-bearing cells, thereby impeding the autoimmune response against host islet cells. Howell et al. (Science 246: 668-70, 1989) have demonstrated that T cell receptor peptides can block the formation of the tri-molecular complex between T cells, autoantigen and major histocompatibilty complex in an autoimmune disease model.
Antibodies and binding partners of the present invention may be used in a variety of ways. The tissue distribution of the islet cell antigen, for example, may be determined by incubating tissue slices with a labeled monoclonal antibody which specifically binds to the islet cell antigen polypeptides, followed by detection of the presence of the bound antibody. Labels suitable for use within the present invention are well known in the art and include, among others, fluorescein, isothiocyanate, phycoerythrin, horseradish peroxidase, and colloidal gold. The antibodies of the present invention may also be used for the purification of the islet cell antigen polypeptides of the present invention. The coupling of antibodies to solid supports and their use in purification of proteins is well known in the literature (see for example, Methods in Molecular Biology, Vol. 1, Walker (Ed.), Humana Press, New Jersey, 1984, which is incorporated by reference herein in its entirety) Antibodies of the present invention may be used as a marker reagent to detect the presence of islet cell antigen polypeptides on cells or in solution. Such antibodies are also useful for western analysis or immunoblotting, particularly of purified cell secreted material. Polyclonal, affinity purified polyclonal, monoclonal and single chain antibodies are suitable for use in this regard. In addition, proteolytic and recombinant fragments and epitope binding domains can be used herein. Chimeric, humanized, veneered, CDR-replaced, reshaped or other recombinant whole or partial antibodies are also suitable.
The following examples are offered by way of illustration, not by way of limitation.